Studies are continuing on the pharmacokinetics and biotransformation of Nor-LAAM. After a 0.5 mg/kg (i.v.) dose of aceylnormethadol (ANM) to 4 rhesus monkeys, the, plasma levels of ANM (mean plus or minus s.e.m.) 5 min. after injection 222 plus or minus 43 ng/ml declined to 6 plus or minus 1 ng/ml b y 24 h. The t 1/2 B and B were 5.13 h. and 0.135h-1 respectively and the apparent volume of distribution was 3.03 1/kg. The urinary and fecal excretion of ANM (% of dose) over a 1 week period was 1.22 plus or minus 0.09 and 5.29 plus or minus 0.09 respectively and total radioactivity 25.44 and 57.43 respectively. The renal and total body clearance (ml/min./kg) were 0.086 and 7.16 respectively. After p.o. administration of the same dose of ANM, the peak plasma levels 14.3 plus or minus 2.2 ng/ml at 2h. declined to 2.8 plus or minus 0.5 ng/ml by 24h. The systemic availability of ANM by p.o administration was 16.5% Higher metabolites to free drug ratio in plasma 0.5 and 1h. after oral dose (1,14,8 as compared to those after i.v. inj. (0.65,0.58) indicated extensive first-pass effect. The urinary and fecal excretion of ANM (% of dose) over a 1 week period after p.o. dose was 0.61 plus or minus 0.11 and 15.75 plus or minus 2.55 respectively and total radioactivity 32.51, 75.01, respectively. Column, t.1.c. and gc/ms. analysis provided evidence for the presence of cyclic pyrrolidine and small amounts of p-OH pyrroline, normethadol and bisnormethadol as free and glucuronide-conjugated urinary metabolites.